Present day electronic applications commonly include PCB mounted components, such as chips or microprocessors, that generate much heat and that are also very sensitive to overheating and therefore require optimum cooling to be maintained at acceptable operating temperatures. One important prerequisite for achieving effective cooling is to optimize thermal contact between the component and the heat sink by minimizing thermal resistance of the joint between the heat transfer contact surfaces of the heat sink and the component. This is generally achieved with good surface structure and measurement precision and parallelism between the component and heat sinks surfaces. In theory, acceptable thermal resistance values would be achievable by securing flatness of as well as parallelism between the surfaces and by producing high surface finish for both surfaces. In practice, however, it would be far too expensive to produce a surface finish that would sufficiently reduce the interstitial air caught in gaps formed between the contact points of even polished surfaces.
Although good surface structure can be achieved by machining, e.g. of the commonly used aluminum heat sink, it is also a fact that in practical applications parallelism between the contact surfaces and height of the component surface above a PCB is often not very exact, being dependent on i.a. soldering joints. For the above reasons, it is common practice to improve the thermal contact by providing thermal interface material, such as thermal grease, thermal tape, thermal phase change material and various thermally conductive gap filler materials, between the contact surfaces to fill the microscopic gaps formed by the roughness of the surfaces and to thereby increase the heat transfer from the component to the heat sink. However, gap filler or other thermal interface material shall not be used to fill “large gaps” since the conductivity is not good enough. A gap-filler shall likewise not be used to compensate for dynamic changes of the gaps, caused e.g. by shock or vibration.
Thermal contact between heat sink and component is dependent also on the contact pressure, and in this context higher contact pressure means smaller gaps and hence better contact. Resilient clamp and/or spring attachments are therefore often used to hold together component and heat sink and to provide appropriate contact pressure for ensuring intimate thermal contact between the contact surfaces, without putting excessive load on either component or printed circuit board.
One problem associated with today's cooling assemblies for heat generating electronic applications is that the integrity of the thermal interface between the component and the heat sink may become disturbed or even destroyed both during transport of the application and during its operation. A cause of such problems is the dynamic dimensional changes that may occur in different environments, such as by differential thermal expansion/contraction or by changes in air humidity affecting plastic materials. Such problems may also occur if an application is subjected to mechanical shock during transport, in its normal operational environment, by accident or even caused by natural forces, such as assemblies operating in areas subjected to earthquakes. The problem is quite obviously aggravated in applications having small size highly heat generating components that for their cooling require comparatively large and heavy heat sinks. Due to the great mass of the heat sink and its large extension past the component contact surface, even moderate shock may destroy the intimate contact between the component and the heat sink and thereby be detrimental to the thermal interface there between.